ViewController constraints in UIScrollView, using Storyboard - ios

Question

I have two UIViewControllers with Storyboard identifiers "vc0" and "vc1", which I am trying to instantiate objects of within a UIScrollView with paging enabled such that the two view controllers are adjacent to each other. The goal is to have the user swipe left and right to swipe between view controllers, similar to SnapChat.
When running my code, the first page of the scrollview contains the first view controller, while the second page contains nothing at all. I am assuming that this is because the first view controller is overlapping the second. How can I alter my constraints (or anything at all) to fix this issue, so that the right edge of vc0 meets with the left edge of vc1?
The UIScrollView is contained within a UIView, within a view controller. Here is the viewDidLoad() which contains all the relevant code. Please let me know of any additional helpful information I should provide.
override func viewDidLoad()
{
super.viewDidLoad()
let screenWidth = self.view.frame.width
let screenHeight = self.view.frame.height
let vc0 = self.storyboard?.instantiateViewControllerWithIdentifier("vc0")
self.addChildViewController(vc0!)
self.scrollView.addSubview(vc0!.view)
vc0!.didMoveToParentViewController(self)
let vc1 = self.storyboard?.instantiateViewControllerWithIdentifier("vc1")
var frame1 = vc1!.view.frame
frame1.origin.x = self.view.frame.size.width
vc1!.view.frame = frame1
self.addChildViewController(vc1!)
self.scrollView.addSubview(vc1!.view)
vc1!.didMoveToParentViewController(self)
self.scrollView.contentSize = CGSizeMake(self.view.frame.size.width * 2, self.view.frame.size.height);
//ADD CONSTRAINTS TO vc0
vc0!.view.translatesAutoresizingMaskIntoConstraints = false
let horizontalConstraint = NSLayoutConstraint(item: vc0!.view, attribute: NSLayoutAttribute.Left, relatedBy: NSLayoutRelation.Equal, toItem: scrollView, attribute: NSLayoutAttribute.Left, multiplier: 1, constant: 0)
view.addConstraint(horizontalConstraint)
let widthConstraint = NSLayoutConstraint(item: vc0!.view, attribute: NSLayoutAttribute.Width, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1, constant: screenWidth)
view.addConstraint(widthConstraint)
let heightConstraint = NSLayoutConstraint(item: vc0!.view, attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1, constant: screenHeight)
view.addConstraint(heightConstraint)
//ADD CONSTRAINTS TO vc1
vc1!.view.translatesAutoresizingMaskIntoConstraints = false
let horizontalConstraint2 = NSLayoutConstraint(item: vc1!.view, attribute: NSLayoutAttribute.Left, relatedBy: NSLayoutRelation.Equal, toItem: vc0!.view, attribute: NSLayoutAttribute.Right, multiplier: 1, constant: 0)
view.addConstraint(horizontalConstraint2)
let widthConstraint2 = NSLayoutConstraint(item: vc1!.view, attribute: NSLayoutAttribute.Width, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1, constant: screenWidth)
view.addConstraint(widthConstraint)
let heightConstraint2 = NSLayoutConstraint(item: vc1!.view, attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1, constant: screenHeight)
view.addConstraint(heightConstraint)
}

Answer 1

I think there is a problem in constraints!!
You should add one view to scrollview and then add views of both VC to that view not direct to scrollview.
view's size should be same as scrollview's contentsize
Now your constrains should be like :
scrollview : top,bottom,leading,trailing
View in scrollview : top,bottom,leading,trailing, Vertical center in container(center Y) and fixed width (because you want horizontal scrolling), If want vertical scrolling then constraint should be (horizontal center in container (center X) and fixed height).
And you views from both VCs : top,leading,fixed width, fixed height (width and height should be same as screen size)
Hope this will help :)